A traditional display device controls pixels by driving a thin film transistor (TFT) on a panel using an external driver chip circuit, thereby to display an image. Along with the development of technologies, the display device has recently been evolved into a structure where a driver circuit, instead of the external driver chip circuit, is directly formed on the panel, so as to reduce the number of elements and the production cost for the traditional display device. For example, such a technology as integrating a gate driver circuit capable of controlling an on/off state of a gate electrode of the TFT into the panel, i.e., a gate driver on array (GOA) technology, is applied.
As shown in FIG. 1, in a circuit design for the existing display device, a charge pump circuit 10 outputs a gate driving voltage, which includes a gate turning-on voltage VGH and a gate turning-off voltage VGL, to a shift register 12 of a gate driver circuit 11, so as to enable a display panel 13 to display the image normally. However, during the manufacture of the display device, the gate driving voltage outputted by the charge pump circuit 10 is usually a constant value, and after the display device operates for a long period of time, a turning-on current Ion of the TFT is decreased obviously and a turning-off current Ioff is increased obviously, so an on-off ratio of the TFT is reduced and the voltage of the gate driver circuit is insufficient to enable the TFT to operate normally. As a result, each pixel is charged insufficiently, resulting in a degradation of the display quality and a reduction in the service life of the display device. This defect is particularly obvious when the TFT is an a-Si TFT.